Diaphragm control apparatus of interchangeable lens camera

ABSTRACT

A diaphragm control apparatus in a camera body includes a stepping motor, a lead screw thereof, wherein a slider is driven by the lead screw, a position detector, and a controller. When the stepping motor is in a free state, the slider allows a diaphragm operatively-associated rod to move to an initial position. The controller detects the slider origin position when the stepping motor is in the free state and drives the stepping motor stepwise to move the slider away from the origin position against a biasing force of a resilient biaser, and drives the stepping motor stepwise to move the slider toward the origin position while detecting the slider position; and sets an initial excitation pattern of the stepping motor upon a distance from the detected slider position to the origin position becoming less than a slider moving distance for one step of the stepping motor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a diaphragm control apparatus of aninterchangeable lens camera, and in particular, relates to a diaphragmcontrol apparatus which enables an adjustable diaphragm of aninterchangeable lens (attached to a camera body) to be controlled by thecamera body during exposure in an interchangeable lens SLR camerasystem.

2. Description of the Related Art

Diaphragm mechanisms (i.e., aperture mechanisms) of conventionalinterchangeable lens SLR camera systems are configured in a manner sothat a diaphragm control bar, which constitutes an element of adiaphragm control mechanism of a camera body, moves a diaphragmoperatively-associated rod of the interchangeable lens that is providedto drive a diaphragm mechanism of the interchangeable lens. In the casewhere the diaphragm control mechanism is powered by a motor of a mirrordrive mechanism or a shutter charge mechanism, the diaphragm can becontrolled only in a single direction due to the structure of thediaphragm control mechanism. For instance, the diaphragm controlmechanism controls the operation of the diaphragm in such a manner as todrive the diaphragm in a diaphragm stop-down direction from anopen-aperture (full-aperture) state and subsequently stops the stop-downmovement of the diaphragm with a ratchet when the diaphragm is stoppeddown to a previously-set aperture value (i.e., f-number), andaccordingly, the f-number of the diaphragm cannot be adjustedafterwards.

In such conventional diaphragm mechanisms, when a live-view operation,in which image data obtained from an image sensor (image pickup device)is displayed on a display monitor in real time, or a movie shootingoperation is performed, the f-number cannot be adjusted from aninitially-set f-number.

In order to enable an f-number adjustment during a live-view operation,the assignee of the prevent invention has proposed an invention forcontrolling the operation of an adjustable diaphragm so as to open andshut the adjustable diaphragm with the use of a diaphragm drive motorserving as a driving source of a diaphragm control mechanism (JapaneseUnexamined Patent Publication 2008-197552). This related invention makesit possible to make an adjustment to a diaphragm setting during alive-view operation or a movie shooting operation.

In conventional interchangeable lenses, the open-aperture referenceposition of the diaphragm operatively-associated rod varies depending onthe f-number at open aperture. Therefore, when an interchangeable lensis attached to a camera body, the amount of movement of the diaphragmcontrol rod, which is provided in the camera body, by the diaphragmoperatively-associated rod varies depending on the type ofinterchangeable lens attached to the camera body. in the case where astepping motor is used as a driving source of the diaphragm controlmechanism, the stepping motor is forced to rotate in association withmovements of the diaphragm control rod; however, the amount of rotationof the stepping motor varies depending on the type of interchangeablelens attached to the camera body. As a result, the stepping motor (therotor thereof) rotates from the initial detent position thereof, makingthe stop position of the stepping motor uncertain. Additionally, inconventional interchangeable lenses, it is sometimes the case that theopen-aperture reference position of the diaphragm operatively-associatedrod, i.e., the initial position thereof relative to a camera body whenan interchangeable lens is attached to the camera body, may be erroneousdue to mechanical error or assembling error, etc. In such a case also,due to this positional error, it is sometimes the case that the stopposition of the stepping motor deviates from the preset initial positionthereof.

Stepping motors that can be utilized as diaphragm drive motors areusually of a type which is driven to rotate by steps in one direction,normally by being repeatedly energized with a plurality of excitationpatterns in order. In this type of stepping motor, if the stop positionand the phase of the excitation pattern do not coincide with each other,a problem occurs with the stepping motor possibly rotating in adirection reverse to the required rotational direction, or even notrotating at all, which causes a mismatch between the number ofexcitations and the number of steps for driving the stepping motor, thuscausing an error in f-number control.

In the case of bringing the stepping motor into a free state by cuttingoff the power applied to the stepping motor after driving the steppingmotor stepwise until the motion of the diaphragm control mechanism ismechanically restricted to detect the initial excitation pattern of thestop position (herein referred as the “origin position”) of the steppingmotor, there is a possibility of the stop position of the stepping motorbecoming unstable upon the stepping motor entering a free state because,e.g., some components of the diaphragm control mechanism may be deformedby the torque and the inertial force of the stepping motor, and therestoring force of such elements may force the stepping motor to rotatein reverse upon the stepping motor entering a free state.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above describedproblems of the prior art and provides a diaphragm control apparatus ofan interchangeable lens camera, wherein the diaphragm control apparatusmakes it possible to perform continuous diaphragm control duringexposure even if an interchangeable lens that is equipped with adiaphragm operatively-associated rod is attached to the camera body, andfurther makes it possible to perform precise stepping-drive control forthe diaphragm even if a stepping motor is used as a driving source ofthe diaphragm control apparatus.

According to an aspect of the present invention, a diaphragm controlapparatus, is provided, incorporated in a camera body, to which aninterchangeable lens provided with a diaphragm apparatus is detachablyattached, the diaphragm apparatus including a diaphragmoperatively-associated rod for driving an adjustable diaphragm to openand shut the adjustable diaphragm, and the diaphragm control apparatusincluding a slider that is driven to move the diaphragmoperatively-associated rod. The diaphragm control apparatus includes adiaphragm control mechanism including a stepping motor and a lead screwwhich is driven to rotate by the stepping motor, wherein the slider ismoved via rotation of the lead screw; a position detector, which detectsa position of the slider; and a controller, which controls an excitationpattern of the stepping motor. The slider is biased to move toward aninitial position by a resilient biaser. When the stepping motor is in afree state with the interchangeable lens attached to the camera body,the slider allows the diaphragm operatively-associated rod to move tothe initial position by a biasing force of the resilient biaser thatbiases the slider toward the initial position while rotating the leadscrew and the stepping motor. The controller detects a position of theslider as an origin position thereof via the position detector when thestepping motor is in the free state. The controller drives the steppingmotor stepwise by a predetermined number of steps in a direction to movethe slider away from the origin position against the biasing force ofthe resilient biaser, and thereafter drives the stepping motor stepwisein a direction to move the slider toward the origin position whiledetecting a position of the slider via the position detector. Thecontroller performs an origin-position initialization process which setsan initial excitation pattern of the stepping motor upon a distance fromthe detected position of the slider to the origin position becoming lessthan a moving distance of the slider for one step of the stepping motor.

It is desirable for the controller to cause the stepping motor to entera free state upon the detected position of the slider, which is detectedvia the position detector, becoming less than the moving distance. Thecontroller thereafter detects a position of the slider to set theinitial excitation pattern of the stepping motor from a differencebetween a position of the slider which is detected in an energized stateand a position of the slider which is detected in the free state of thestepping motor, and also from a moving distance of the slider whenstepping motor is driven by one step.

It is desirable for the stepping motor to be of a type which moves theslider stepwise one of toward and away from the origin position by beingrepeatedly energized with a plurality of excitation patterns in one ofpredetermined forward and reverse orders, and for the controller tocommence a stepwise driving of the stepping motor with the slider beingpositioned at the origin position from the initial excitation pattern ina forward stroke of a reciprocating motion of the slider, and return theslider to the origin position by repeatedly energizing the steppingmotor with the plurality of excitation patterns firstly a predeterminednumber of times in a predetermined order and subsequently in a reverseorder in a backward stroke of the reciprocating motion of the slider.

It is desirable for the controller to detect the moving distance bywhich the slider moves from the origin position by one step of thestepping motor during the forward-stroke of the reciprocating motion ofthe slider, in which the controller drives the stepping motor stepwisein the direction to move the slider away from the origin position, toset a threshold value that is less than the moving distance by which theslider moves from the origin position by one step of the stepping motor.Thereafter, the controller detects a position of the slider each timethe stepping motor is driven by one step in the backward stroke of thereciprocating motion of the slider, in which the controller drives thestepping motor stepwise in the direction to move the slider toward theorigin position. Upon the position of the slider detected by thecontroller reaching a position in between the threshold value and theorigin position, the controller detects a position of the slider whileholding energization of the stepping motor, and thereafter cuts off theenergization of the stepping motor to cause the stepping motor to entera free state.

It is desirable for the position detector to include at least one magnetand a Hall sensor.

It is desirable for the slider to be supported by a slide shaft thatextends parallel to the lead screw so that the slider is freely slidablethereon, and for the magnet to be installed onto the slider at aposition between the lead screw and the slide shaft.

It is desirable for the diaphragm apparatus of the interchangeable lensto include a diaphragm ring, positioned coaxially with an optical axisof the interchangeable lens, to be rotatable about the optical axis, thediaphragm operatively-associated rod being integrally formed with thediaphragm ring to project rearward from a rear end of theinterchangeable lens. The diaphragm ring is continuously biased by abiaser in a direction to stop down an aperture formed by diaphragmblades of the diaphragm apparatus.

According to the present invention, due to the above describedstructure, even when the rotational position of the stepping motorbecomes uncertain as a result of the slider being forced to move tothereby rotate the stepping motor, the rotational position of thestepping motor can be initialized with precision because it takes lessthan one step of movement of the stepping motor until the rotation ofthe stepping motor is mechanically stopped and thereafter the steppingmotor rotates only less than one step.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 2009-151410 (filed on Jun. 25, 2009) and JapanesePatent Application No. 2010-139363 (filed on Jun. 18, 2010) which areexpressly incorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a front elevational view of a camera body of an SLR camerasystem according to the present invention;

FIG. 2A is a rear elevational view of an interchangeable lens that isattachable to the camera body and is provided with a diaphragminterlocking rod;

FIG. 2B is a side elevational view of the interchangeable lens shown inFIG. 2A;

FIG. 3 is a block diagram showing main elements of the SLR camera systemwith the interchangeable lens attached to the camera body;

FIG. 4 is a rear elevational view, as viewed from the camera body side)of a diaphragm control mechanism of the camera body and main elements ofa diaphragm apparatus provided in the interchangeable lens, showing thediaphragm control mechanism and the diaphragm apparatus in afull-aperture state;

FIG. 5 is a view similar to that of FIG. 4, showing the diaphragmcontrol mechanism and the diaphragm apparatus in a fully stopped-downstate;

FIGS. 6A and 6B are perspective views of the diaphragm control mechanismof the camera body with the diaphragm apparatus in an open-aperturestate, viewed obliquely from the front left-hand side and the frontright-hand side, respectively;

FIGS. 7A and 7B are perspective views of the diaphragm control mechanismof the camera body with a slider which constitutes an element of thediaphragm control mechanism being removed for clarity, viewed obliquelyfrom the front left-hand side and the front right-hand side,respectively;

FIG. 8 is a schematic side view of an embodiment of a position detector,composed of a Hall sensor and a pair of magnets, incorporated in thediaphragm control mechanism for detecting the initial position of theslider of the diaphragm control mechanism;

FIG. 9 is a timing chart showing the overall operation of the diaphragmcontrol mechanism for the origin-position initialization process for thediaphragm control mechanism shown in FIGS. 11 through 14;

FIG. 10 is a timing chart showing operations in the origin-positioninitialization process which are performed from the moment that theslider returns to a position in the close vicinity of the originposition thereof;

FIGS. 11A and 11B show a flow chart showing operations of theorigin-position initialization process for the diaphragm controlmechanism;

FIG. 12 is a flow chart showing operations of the origin-positioninitialization process for the diaphragm control mechanism;

FIGS. 13A and 13B show a flow chart showing operations of theorigin-position initialization process for the diaphragm controlmechanism; and

FIG. 14 is a flow chart showing operations of the origin-positioninitialization process for the diaphragm control mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of an SLR camera system according to the present inventionis provided with a camera body 10 and an interchangeable lens(photographic lens) 100 that is detachably attached to the camera body10. A body mount (mount ring) 13 is fixed to an approximate center ofthe front of the camera body 10. The camera body 10 is provided on thesurface of the body mount 13 with an AF coupler 14, a group ofinformation contacts 15, a lock pin 16 and a mount index mark 17. Thecamera body 10 is provided on an inner periphery of the body mount 13with a bayonet mount 18. The camera body 10 is provided in a mirror boxthereof with a main mirror 20, and is provided, on the left hand side ofthe main mirror 20 with respect to FIG. 1 in the vicinity of the bayonetmount 18, with a diaphragm control rod 19 for controlling movements of adiaphragm operatively-associated rod 109 of the interchangeable lens 100(see FIGS. 2A and 2B).

The camera body 10 is provided, on the top left thereof with respect toFIG. 1, with a shutter release button 21, and is provided around theshutter release button 21 with a rotary ring-shaped power switch 23. Thecamera body 10 is provided, on top right thereof with respect to FIG. 1,with a mode dial 25.

The power switch 23 is structured to be manually rotatable. The powerswitch 23 is click-stopped at the power OFF position and at the power ONposition, and can be turned to a live-view position (set on the oppositeside of the power ON position from the power OFF position) against aspring biasing force. If the power switch 23 is further turned towardthe live-view position from the power ON position, the live-view switchis turned ON while the power remains switched ON.

The mode dial 25 is a rotary switch which stops with a tactile click ateach of a plurality of different stop positions. Various exposure modessuch as a still-image photographing mode and a movie recording mode canbe selected (switched) according to the click-stop position of the modedial 25.

The interchangeable lens 100 is provided at the rear end thereof with alens mount ring 103. The interchangeable lens 100 is provided on thesurface of the lens mount ring 103 with an AF coupler 104, a group ofinformation contacts 105 and a lock hole 106 which correspond to the AFcoupler 14, the group of information contacts 15 and the lock pin 16,respectively, that are provided on the surface of the body mount 13. Theinterchangeable lens 100 is provided on an inner periphery of the lensmount ring 103 with a bayonet mount 108. The interchangeable lens 100 isfurther provided immediately inside (radially inside) an innerperipheral surface of the bayonet mount 108 with the diaphragmoperatively-associated rod 109 that is interlocked with the diaphragmcontrol rod 19 of the camera body 10 when the interchangeable lens 100is properly mounted onto the camera body 10. The interchangeable lens100 is provided thereon with amount index mark 107 which corresponds tothe mount index mark 17 of the camera body 10.

When the interchangeable lens 100 is attached to the camera body 10, thebayonet mounts 18 and 108 are brought into engagement with each otherwith the mount index marks 17 and 107 being aligned with each other, andsubsequently the interchangeable lens 100 is rotated clockwise relativeto the camera body 10 as viewed from front of the camera body 10. Thisclockwise rotation of the interchangeable lens 100 relative to thecamera body 10 causes the diaphragm operatively-associated rod 109 ofthe interchangeable lens 100 to come into contact with the diaphragmcontrol rod 19 of the camera body 10; a further clockwise rotation ofthe interchangeable lens 100 causes the diaphragm control rod 19 to movedue to the engagement of the diaphragm control rod 19 with the diaphragmoperatively-associated rod 109; and a subsequently further clockwiserotation of the interchangeable lens 100 causes the lock pin 16 to beengaged in the lock hole 106 with a click at a locked position, wherebythe interchangeable lens 100 stops rotating relative to the camera body10 so that the interchangeable lens 10 becomes properly mounted onto thecamera body 10. In this locked position, the diaphragmoperatively-associated rod 109 abuts against one end of the moving rangethereof, thus being prevented from moving. This position of thediaphragm operatively-associated rod 109 corresponds to theopen-aperture reference position thereof. On the other hand, thediaphragm control rod 19 has been forcibly moved from the initialposition thereof to a position corresponding to the open-aperturereference position of the diaphragm operatively-associated rod 109. In astate where the interchangeable lens 100 is locked in this lockedposition, the AF coupler 104 is engaged with the AF coupler 14, and thegroup of information contacts 105 is in electrical contact with thegroup of information contacts 15.

FIG. 3 is a schematic block diagram showing main elements of the camerabody 10 and the interchangeable lens 100 that is attached to the camerabody 10. The camera body 10 is provided above the main mirror 20 with afocusing screen 27, a pentagonal prism 28 and an eyepiece 29, whichserve as elements of an optical viewfinder through which an object imageformed through the interchangeable lens 100 is viewed. The camera body10 is provided in the vicinity of the eyepiece 29 with a photo meteringelement 30 for measuring object brightness.

The camera body 10 is provided behind the main mirror 20 with an imagesensor (image pickup device) 31, such as a CCD image sensor whichreceives object light upon the main mirror 20 being raised to theretracted position (mirror-up position) to capture an object image, andis provided immediately in front of the image sensor 31 with a shuttermechanism 33. The camera body 10 is provided, immediately behind ahalf-mirror portion formed at a central portion of the main mirror 20,with a sub-mirror 35 which reflects incident object light downward. Thecamera body 10 is provided, below the sub-mirror 35 at the bottom of themirror box, with an AF unit 37 which receives the object light reflectedby the sub-mirror 35 to detect a focus state. The AF unit 37 is aso-called TTL phase-difference detector that outputs a pair of objectimage signals, which) 45 provided in the camera body 10 calculates adefocus amount from this AF data, and further calculates data necessaryfor moving a focusing lens group of the interchangeable lens attached tothe camera body 10.

The camera, body 10 is provided therein with a signal processor 39. Thesignal processor 39 processes image signals obtained by an imagecapturing operation of the image sensor 31, compresses or does notcompress the processed image signals, and stores the image signals thuscompressed or not compressed in an image memory 41 provided in thecamera body 10. The camera body 10 is provided on the back thereof witha display 43 (e.g., an LCD panel) which displays captured images. Theimage displaying operation of the display 43 is controlled by the signalprocessor 39.

The camera body 10 is provided with an AF system 47 and a diaphragmcontrol mechanism (diaphragm control apparatus) 51. The AF system 47drives an AF mechanism 111 of the interchangeable lens 100, and thediaphragm control mechanism 51 controls the operation of a diaphragmapparatus 113 of the interchangeable lens 100. The AF system 47incorporates an AF motor (not shown) and transmits rotation of this AFmotor to the AF mechanism 111 of the interchangeable lens 100 via the AFcouplers 14 and 104. The operation of this AF motor is controlled by theCPU 45, and the AF mechanism 111 moves a focusing lens group LF of aphotographing optical system L (see FIG. 3) of the interchangeable lens100 to an in-focus position. The operation of the diaphragm controlmechanism 51 is controlled by the CPU 45 via a diaphragm drive circuit49 provided in the camera body 10 to drive the diaphragm control rod 19.

In addition, photometric data output from the photometering element 30and AF data output from the AF unit 37 are input to the CPU 45. Based onsuch data, the CPU 45 calculates appropriate data for the f-number andappropriate lens drive data for focusing, drives the diaphragm controlmechanism 51 via the diaphragm drive circuit 49 in accordance with thecalculated data on f-number, and drives the AF system 47 in accordancewith the calculated lens drive data.

The diaphragm apparatus 113 of the interchangeable lens 100 operates toadjust the amount of light passing through a diaphragm aperture formedby a plurality of diaphragm blades 115 by opening and shutting theplurality of diaphragm blades 115. The diaphragm apparatus 113 isprovided with the diaphragm operatively-associated rod 109, as describedabove, and the opening and shutting operation of the plurality ofdiaphragm blades 115 is controlled via the diaphragmoperatively-associated rod 109.

[Diaphragm Control Mechanism]

The structures of the diaphragm control mechanism 51 of the camera body10 and the diaphragm apparatus 113 of the interchangeable lens 100 willbe discussed in detail with reference to FIGS. 4 through 8. FIG. 4 is arear elevational view of the diaphragm control mechanism 51 and mainelements of the diaphragm apparatus 113 in a full-aperture state; FIG. 5is a rear elevational view of the diaphragm control mechanism 51 andmain elements of the diaphragm apparatus 113 in a fully stopped-downstate; FIG. 6A is a perspective view of the diaphragm control mechanism51 with the diaphragm apparatus 113 in an open-aperture state, viewedobliquely from the front left-hand side; FIG. 6B is a perspective viewof the diaphragm control mechanism 51 with the diaphragm apparatus 113in an open-aperture state, viewed obliquely from the front right-handside; FIG. 7A is a perspective view of the diaphragm control mechanism51 with a slider 57 which constitutes an element of the diaphragmcontrol mechanism 51 being removed for clarity, viewed obliquely fromthe front left-hand side; FIG. 7B is a perspective view of the diaphragmcontrol mechanism 51 with the slider 57 being removed for clarity,viewed obliquely from the front right-hand side; and FIG. 8 is aschematic diagram showing an embodiment of a position detector (composedof a Hall sensor and a pair of permanent magnets) for detecting anorigin position of the slider 57.

The diaphragm control mechanism 51 is provided with a stepping motor 53,as a driving source thereof, which has a lead screw 55 as a rotaryshaft. Namely, the lead screw 55 rotates integrally with the rotor ofthe stepping motor 53. The stepping motor 53 is fixed to a frame(stationary member) 59, and the end (lower end with respect to FIGS. 4through 7B) of the lead screw 55 is supported by a lug, projecting fromthe frame 59, so that the lead screw 55 is freely rotatable about theaxis thereof. The frame 59 is fixed to a stationary frame (not shown) ofthe camera body 10.

A screw nut 57 c formed at an end of an arm 57 b extending from theslider 57 is screw-engaged with the lead screw 55. The slider 57 isprovided in a main body 57 a thereof with a shaft hole in which a slideshaft 61 is slidably fitted, so that the slider 57 is supported by theslide shaft 61 to be freely slidable thereon. Both ends of the slideshaft 61 are supported by the frame 59 (an upper portion of the frame 59and a lower lug projected from the frame 59) so that the slide shaft 61extends parallel to the lead screw 55. The diaphragm control rod 19 isformed to project integrally from the main body 57 a of the slider 57,thus moving integrally with the slider 57.

The diaphragm control mechanism 51 can drive the stepping motor 53stepwise to rotate the lead screw 55 stepwise. Namely, the diaphragmcontrol mechanism 51 can integrally move the slider 57 and the diaphragmcontrol rod 19, together with the screw nut 57 c, stepwise in very smalllength units determined by a one-step rotational angle (rotational angleby one excitation step) and the lead of the lead screw 55. The movingrange of the diaphragm control rod 19 in the present embodiment rangesfrom the movement extremity thereof (one end of the moving range thereofon the open-aperture side of an initial position/open-aperture-sidemovable limit), shown in FIGS. 4, at which one end of the slider 57 (inthe sliding direction thereof) comes in contact with a limit portion ofthe frame 59, to the other end of the moving range on the fullystopped-down side (stop-down-side movable limit), at which the other endof the slider 57 (in the sliding direction thereof) comes in contactwith the other limit portion of the frame 59. FIG. 5 shows the fullystopped-down position of the interchangeable lens 100, and the slider 57can further move upward from the position shown in FIG. 5 until theaforementioned other end of the slider 57 comes into contact with theaforementioned another limit portion of the frame 59.

The diaphragm control mechanism 51 is provided with a biasing spring(resilient biaser) 67 as a resilient biaser which biases the slider 57in a direction toward the origin position (the open-aperture-sidemovable limit). The biasing spring 67 is configured from a torsionspring that is provided with a coiled portion 67 a at a middle partthereof. The coiled portion 67 a of the biasing spring 67 is fitted on amount pin 70 which projects from a mount (stationary member) 68. Themount 68 is fixed to the frame 59 via a mount plate 69. One end 67 b ofthe biasing spring 67 that extends from the coiled portion 67 a isengaged with an engaging portion 57 d, which projects from the slider57, while the other end 67 c of the biasing spring 67 that also extendsfrom the coiled portion 67 a is engaged with the mount 68 so that theslider 57 is continuously biased toward the aperture opening direction(downward direction with respect to FIG. 4). The slider 57 can move bythe biasing force of the biasing spring 67 to the open-aperture-sidemovable limit, at which the slider 57 is mechanically prevented frommoving beyond the open-aperture-side movable limit, by rotating the leadscrew 55 and the stepping motor 53 in a state (free state) where nocurrent is passed through the stepping motor 53. Even with theinterchangeable lens 100 mounted to the camera body 10, the biasingforce of the biasing spring 67 is predetermined to be normally capableof moving the slider 57 to the open-aperture-side movable limit againstthe biasing force of a diaphragm spring (extension coil spring/biaser)121 (see FIGS. 4 and 5) of the interchangeable lens 100, and to allowthe stepping motor 53 to move the slider 57 to the stop-down-sidemovable limit.

The slider 57 is mechanically prevented from moving from theopen-aperture-side movable limit (the initial position) by the biasingforce of the biasing spring 67 when no interchangeable lens is attachedto the camera body 10; therefore, the stop position of the steppingmotor 53 is also constant.

The interchangeable lens 100 is mounted to the camera body 10 by beingmanually rotated in a direction shown by the arrow α in FIG. 2A(counterclockwise direction with respect to FIG. 2A) with respect to thecamera body 10. In this mounting operation, the diaphragmoperatively-associated rod 109 comes in contact with the diaphragmcontrol rod 19 and the counterclockwise rotation of the interchangeablelens 100 with respect to the camera body 10 causes the diaphragm controlrod 19 and the slider 57 to move to positions thereof corresponding tothe open-aperture reference position of the diaphragmoperatively-associated rod 109 (to the positions shown in FIG. 4).Namely, since the diaphragm operatively-associated rod 109 stops at theopen-aperture reference position thereof, where the diaphragmoperatively-associated rod 109 is mechanically prevented from moving,the diaphragm control rod 19 which is in contact with the diaphragmoperatively-associated rod 109 is moved with the slider 57 in adiaphragm stop-down direction (direction to stop down the diaphragmmechanism 119) against the biasing force of the biasing spring 67. Asshown in FIG. 4, the diaphragm control rod 19 (the slider 57) in thepresent embodiment has been moved by a displacement Ad from the initialposition to the origin position in the diaphragm stop-down direction(upward direction with respect to FIG. 4). Due to this movement of thediaphragm control rod 19, the stepping motor 53 has been rotated by arotation angle corresponding to the displacement Ad divided by the leadof the lead screw 55. Therefore, when the interchangeable lens 100 isattached to the camera body 10, the stop position of the stepping motor53, which serves as an origin position (initial excitation pattern ofthe stop position) thereof, becomes unclear.

If the origin position of the stepping motor 53 becomes unclear, itbecomes unclear as to which excitation pattern (NO.) the stepping motor53 should commence to be excited from, in order to rotate the steppingmotor 53 stepwise from the first excitation. In the present embodimentof the SLR camera system, an appropriate first excitation phase can beset by detecting the position at which the stepping motor 53 thus forcedto rotate is currently at rest, and by detecting the excitation pattern(NO.) from which the stepping motor 53 should commence to be excited;i.e., by detecting the origin position of the stepping motor 53.Features of this embodiment will be discussed hereinafter.

The diaphragm control mechanism 51 is provided with a pair of magnets 64(64 a and 64 b) and a Hall sensor 65 (see FIG. 8) that serve as elementsof an origin position detection sensor (position detector) 63 fordetecting the origin position of the slider 57. The magnets 64 a and 64b are fixed to the arm 57 b of the slider 57, which is provided betweenthe lead screw 55 and the slide shaft 61, and the Hall sensor 65 ismounted on a sensor board 66 that is fixed to the frame 59. If theorigin position detection sensor 63 uses a Hall element having anauto-compensation function, the influences and errors caused byenvironmental conditions and secular changes can be minimized.

The Hall sensor 65 senses a magnetic force from the magnets 64 (64 a and64 b) and outputs a voltage according to this magnetic force. The CPU 45detects the position of the magnets 64 a and 64 b, i.e., the position ofthe slider 57, and hence, the position of the diaphragm control rod 19,in accordance with a detection signal output from the Hall sensor 65.Since the Hall sensor 65 outputs a detection signal according to thedistance from the Hall sensor 65 to the pair of magnets 64 a and 64 b,the relative distance between the Hall sensor 65 and the pair of magnets64 a and 64 b can be detected within a predetermined range. The magnets64 a and 64 b and the Hall sensor 65 are arranged so as to detect anorigin position of the slider 57 corresponding to the open-aperturereference position of the diaphragm operatively-associated rod of theinterchangeable lens equipped with the slider 57.

FIG. 8 schematically shows the structure of an embodiment of the originposition detection sensor 63 of the diaphragm control mechanism 51. Inthis drawing, the leftward/rightward direction corresponds to the movingdirection of the pair of magnets 64 a and 64 b.

In the embodiment shown in FIG. 8, the two magnets 64 a and 64 b arejoined together and arranged along the moving direction thereof so thatopposite poles of the two magnets 64 a and 64 b face the Hall sensor 65.According to this structure, a magnetic force of the two magnets 64 aand 64 b exits out of the center of the surface of the N-pole of themagnet 64 b which faces the Hall sensor 65 and enters into the center ofthe surface of the S-pole of the magnet 64 a which faces the Hall sensor65, as shown in FIG. 8; and accordingly, the magnetic force changesabruptly in the relative moving direction (horizontal direction asviewed in FIG. 8), and the sensitivity of the origin position detectionsensor 63 becomes acute. It is possible for a single ferromagneticmaterial to be divided into two and for each ferromagnetic materialthereof to be magnetized in a direction orthogonal to the relativemoving direction.

The diaphragm apparatus 113 of the interchangeable lens 100 is providedwith a diaphragm ring 117, the diaphragm operatively-associated rod 109,a linkage rod 118 and a diaphragm mechanism 119. The diaphragm ring 117rotates about an optical axis O of the interchangeable lens 100. Thediaphragm operatively-associated rod 109 of the diaphragm apparatus 113,which is engageable with the diaphragm control rod 19 of the camera body10, projects rearward (toward the camera body 10) from the outer edge ofthe diaphragm ring 117. The linkage rod 118 projects from the inner edgeof the diaphragm ring 117 toward the object side to extend parallel tothe optical axis O. The diaphragm mechanism 119 is provided with aplurality of diaphragm blades (aperture blades) 115. The diaphragmmechanism 119 is a conventional type which drives the plurality ofdiaphragm blades 115 so that they open and shut by receiving arotational movement of the linkage rod 118. In addition, the diaphragmring 117 is biased to rotate in a direction to stop down the pluralityof diaphragm blades 115 by the diaphragm spring 121.

When the camera body 10 is in a natural state and without theinterchangeable lens 100 being mounted thereto, the plurality ofdiaphragm blades 115 (diaphragm ring 117) are fully stopped down by thebiasing force of the diaphragm spring 121, the diaphragm ring 117 isrotatably biased toward the fully stopped down position, which is amechanical rotational limit to which a stopper (not shown) abuts, andthe diaphragm ring 117 is held at this fully stopped down position. Whenthe interchangeable lens 100 is mounted to the camera body 10, in whichthe interchangeable lens 100 is rotated relative to the camera body 10,the diaphragm operatively-associated rod 109 is rotated in the openingdirection against the biasing force of the diaphragm spring 121 via thediaphragm control rod 19; thereafter, upon the interchangeable lens 100being further rotated relative to the camera body 10 until theinterchangeable lens 100 becomes properly mounted onto the camera body10 at the locked position, the diaphragm ring 117 stops at theopen-aperture reference position (initial position), which is amechanical rotational limit to which a stopper (not shown) abuts, andthe diaphragm ring 117 is held thereat. As described above, the slider57, which is integral with the diaphragm control rod 19 of the camerabody 10, is moved from the initial position in the diaphragm stop-downdirection and held at a position (origin position) corresponding to theopen-aperture reference position.

With the above described structure, when no interchangeable lens isattached to the camera body 10 or when the diaphragmoperatively-associated rod 109 is in a free state, the diaphragmapparatus 113 of the interchangeable lens 100 is in a state such thatthe plurality of diaphragm blades 115 of the diaphragm mechanism 119 arefully stopped down by the resilient biasing force of the diaphragmspring 121.

On the other hand, in a state where the interchangeable lens 100 isattached to the camera body 10, e.g., in an initial state shown in FIG.4, the diaphragm operatively-associated rod 109 has been rotated to theopen-aperture reference position (a mechanical rotation limit position)with the diaphragm operatively-associated rod 109 being in contact withthe diaphragm control rod 19 while the diaphragm ring 117 has been fullyrotated in a diaphragm opening direction against the biasing force ofthe diaphragm spring 121 so that the plurality of diaphragm blades 115are held in a fully-open state. In addition, the slider 57 and thediaphragm control rod 19 have been further moved in a diaphragmstop-down direction by the diaphragm operatively-associated rod 109having being rotated to the open-aperture reference position, thusprevented from rotating, and are held at an origin positioncorresponding to the open-aperture reference position of the diaphragmoperatively-associated rod 109.

Thereafter, in a photographing operation, the slider 57 and thediaphragm control rod 19 are moved in the diaphragm stop-down directionby stepwise rotation of the stepping motor 53, and the diaphragmoperatively-associated rod 109 moves in the diaphragm stop-downdirection following the movement of the diaphragm control rod 19 untilreaching a stop position that corresponds to a desired f-number.Thereupon, the stepping motor 53 is held at this stop position, andhence, the f-number corresponding to this stop position is set. Theamount of stop-down of the diaphragm mechanism 119 (f-number) iscontrolled according to the number of steps (excitation pattern (NO.))for driving the stepping motor 53 from the initial position thereof.

The holding force of an excitation holding state of the stepping motor53 is stronger than the difference between the biasing force of thediaphragm spring 121 in the diaphragm stop-down direction, which acts onthe diaphragm control rod 19, and the biasing force of the biasingspring 67 (of the slider 57) in the aperture-opening direction; hence,the slider 57 is held at a stopped position by the holding force of theexcitation holding state of the stepping motor 53.

In this stopped-down state of the diaphragm apparatus 113, the diaphragmcontrol mechanism 51 can drive the stepping motor 53 in eitherdirection, i.e., the diaphragm stop-down direction or the diaphragmopening direction. Namely, diaphragm control during exposure ispossible. Therefore, diaphragm control during a live-view operation or amovie shooting operation is possible.

The origin position detection sensor 63 (composed of the pair of magnets64 a and 64 b and the Hall sensor 65) is configured to be capable ofdetecting, by movements of the diaphragm control rod 19 and the slider57 in the diaphragm stop-down direction from the initial positionsthereof, the initial position of the diaphragm operatively-associatedrod 109 (which corresponds to the open-aperture reference positionthereof) of the interchangeable lens 100 when mounted to the camera body10. The origin position detection sensor 63 is configured and arrangedto be capable of detecting the position of the slider 57 within apredetermined moving range thereof because the f-number at openaperture, i.e., the open-aperture reference position, of the diaphragmoperatively-associated rod 109 varies depending on the type ofphotographing lens or varies due to assembling errors even in the sametype of photographing lens as described above.

In the illustrated embodiment, when the slider 57 and the stepping motor53 are stopped at the origin position corresponding to the open-aperturereference position of the diaphragm operatively-associated rod 109, thedetection of the excitation pattern at the stopped position of thestepping motor 53 or the detection of the initial excitation pattern arereferred to as the “origin-position initialization operation”.

An origin-position initialization process for the diaphragm controlmechanism 51 will be hereinafter discussed with reference to the timingcharts shown in FIGS. 9 and 10 for the driving of the stepping motor 53,and with reference to the flow charts shown in FIGS. 11 through 14.

The stepping motor 53 in the present embodiment is a two-phase steppingmotor which includes two-phase coils X and X− and coils Y and Y−, androtates stepwise with four kinds of excitation patterns. Table 1 belowshows the numbers (identification numbers) of these four kinds ofexcitation patterns (NO.) for the coils X, X−, Y and Y−. In thisembodiment, by repeating the two-phase driving excitation patterns (0),(1), (2), (3) (i.e., by switching energization of the coils X, X−, Y andY−), the stepping motor 53 can be driven stepwise in one direction(diaphragm stop-down direction). In addition, the stepping motor 53 canbe driven stepwise in the other (opposite) direction (diaphragm openingdirection) by repeating the excitation patterns (3), (2), (1), (0).

TABLE 1 NO. (0) (1) (2) (3) X 0 0 1 1 X− 1 1 0 0 Y 0 1 1 0 Y− 1 0 0 1

When the stepping motor 53 is excited with one of the four excitationpatterns (NO.) and thereupon the excitation is cut off to hold thestepping motor 53, the first excitation (NO.) for the subsequent drivingof the stepping motor 53 becomes one before or after the excitationpattern, in accordance with the driving direction of the stepping motor53, at the time of the excitation cutoff. For instance, if the number ofthe excitation pattern (NO.) at the time of an excitation cutoff (at thetime the stepping motor 53 is in a free state) is 0 (when the detentposition is (0)), the subsequent excitation starts from the excitationpattern (1) in the case of driving the stepping motor 53 in thediaphragm stop-down direction, or starts from the excitation pattern (3)in the case of driving the stepping motor 53 in the diaphragm openingdirection. Such an excitation operation is performed by the diaphragmcontrol circuit 49 under the control of the CPU 45. In the presentembodiment, the excitation patterns are switched at a constant pulserate. Namely, the excitation patterns are switched from one excitationpattern to another after a continuation of energization (excitation)with each excitation pattern (NO.) for a fixed period of time t1(several microseconds (ms)).

[Origin-Position Initialization Process]

In this embodiment, the stepping motor 53 is driven so that the slider57 reciprocally moves a predetermined number of steps, and subsequently,the stepping motor 53 is brought into a free state upon the slider 57returning to a position in the vicinity of the origin position thereof.Thereupon, the stop position of the stepping motor 53, after thestepping motor 53 has been rotated by the movement of the slider 57 andstopped, is detected to set this stop position as an origin position andto set the excitation pattern at this origin position as an initialexcitation pattern. An outline description of such operations will behereinafter discussed with reference to the timing charts shown in FIGS.9 and 10.

At the commencement of the origin-position initialization operation, theposition of the slider 57 is detected and stored (in a memory) as theorigin position thereof before the stepping motor 53 is energized.Subsequently, the stepping motor 53 is energized in order, starting fromthe excitation pattern (0) as a reference start-up excitation pattern,to rotate in the diaphragm stop-down direction (direction to move theslider 57 away from the origin position against the biasing force of thebiasing spring 67). Although the stepping motor 53 is energized with theexcitation pattern (0) at the start, the stepping motor 53 does notrotate if previously at rest at the position of the excitation pattern(0), the stepping motor 53 attempts to rotate one step in the diaphragmopening direction if previously at rest at the position of theexcitation pattern (1), the stepping motor 53 does not rotate or rotatein either the diaphragm stop-down direction or the diaphragm openingdirection if previously at rest at the position of the excitationpattern (2), or the stepping motor 53 rotates in the diaphragm openingdirection if previously at rest at the position of the excitationpattern (3). In any of these four cases, the stop position of thestepping motor 53 and the excitation pattern (NO.) coincide with eachother at the third energization at the latest, so that the steppingmotor 53 comes to rotate one step in the diaphragm stop-down directionfrom the fourth energization.

As shown in FIG. 9, the stepping motor 53 is driven a total of eightsteps in the first half (forward stroke) of a reciprocating motion ofthe slider 57 in the present embodiment. In the course of this stepwisedriving, the position of the slider 57 immediately before the excitationat the fifth step (during the excitation with the excitation pattern(3)) and the position of the slider 57 immediately before the excitationat the eighth step (during the excitation with the excitation pattern(2)) are detected to determine a moving distance A of the slider 57 whenthe slider 57 moves three steps. and further to determine the average ofthe moving distance (stepwise moving distance per one step) of theslider 57 when the slider 57 moves one step (by dividing the movingdistance A by three). Therefore, the value obtained by multiplying theaverage value by a predetermined coefficient less than 1 is set as ΔA,and the value obtained by adding ΔA to an origin position value PO isset as a threshold value P0′. Although the coefficient is set at 0.7 inthis embodiment, it is desirable that the coefficient be in the range of0.3 to 0.9. In the calculation of ΔA, the reason why the position of theslider 57 commences to be detected from the position thereof immediatelybefore the excitation at the fifth step (during the excitation with theexcitation pattern (3)) is in order to precisely detect the position ofthe slider 57 in a state after the stepping motor 53 has been certainlyrotated one step through a cycle of the four excitation patterns (0)through (4).

The first half of a reciprocating motion of the slider 57 is completedby excitation of eight steps, and subsequently the latter half (backwardstroke) of the reciprocating motion of the slider 57 commences. In thelatter half of the reciprocating motion of the slider 57, the CPU 45drives the stepping motor 53 stepwise in the diaphragm opening directionwhile detecting the position of the slider 57. In this embodiment, sincethe stepping motor 53 is held with the excitation pattern (3) at theeighth step, the stepping motor 53 starts being driven stepwise in orderfrom the excitation pattern (2) in the latter half of the reciprocatingmotion of the slider 57. Thereafter, every time the stepping motor 53 isdriven one step, it is determined whether or not the detected positionof the slider 57 has become less than the aforementioned threshold valueP0′ immediately before the stepping motor 53 is excited with thesubsequent excitation pattern (NO.). The stepping motor 53 continues tobe driven unless the detected position of the slider 57 has become lessthan the threshold value P0′.

Upon the detection position of the slider 57 becoming less than thethreshold value P0′, the excitation at this time continued (theexcitation for the stepping motor 53 at this time is held) for a longerperiod of time than normal, and upon a lapse of this period of time, theexcitation is stopped. The excitation pattern when the excitation isstopped is the excitation pattern of the origin position, and thisexcitation pattern is stored in memory as the initial excitationpattern. Thereafter, when the diaphragm is stopped down, excitationcommences from the initial excitation pattern or the next excitationpattern thereof. Although the excitation may commence from the nextexcitation pattern after the initial excitation pattern, if excitationcommences from the initial excitation pattern that was set at the startof the stop down operation, the slider 57 can be reliably moved from theorigin position to a position less than the threshold value P0′. In thismanner, according to the origin-position initialization operation in thepresent embodiment, the stepping motor 53 is stopped beforemechanisms/components which are driven by the stepping motor 53mechanically come into collision with each other, and accordingly, thereis no possibility of such driven mechanisms/components being bent by thecollision or undergoing any reaction from the collision. Moreover, bystopping the stepping motor 53 upon detecting that the position of theslider 57 has become less than the threshold value P0′ and by findingthe excitation pattern at this stopped position of the stepping motor53, the excitation pattern, of the stepping motor 53, that should beexcited in the subsequent actuation of the stepping motor 53 can bedetermined.

It is sometimes the case that the slider 57 does not stopinstantaneously, thus slightly moving even after the excitation for thestepping motor 53 is stopped after being held as described above.Therefore, in the present embodiment, by detecting the position of theslider 57 and storing this position in memory immediately before theexcitation is cut off and by again detecting the position of the slider57 upon a lapse of a predetermined period of time from the cutoff of theexcitation, a difference between the position of the slider 57 when itis held by the stepping motor 53 and the position of the slider 57 afterit is released from being held by the stepping motor 53 (i.e., theposition of the slider 57 when it stops after being moved to amechanical moving limit by the biasing force of the biasing spring 67)is determined, and from this difference the excitation pattern (NO.) atthe stop position of the stepping motor 53 is determined and stored inmemory as the initial excitation pattern (NO.). In FIGS. 9 and 10, theinitial excitation pattern (NO.) is (0). In the above describedembodiment, although the threshold value P0′ (ΔA) is set based ondetection results (of the position of the slider 57) when the slider 57is positioned far away from the origin position in the forward stroke ofthe reciprocating motion of the slider 57, the detection of the amountof movement of the slider 57 can be carried out with higher precision ifdetected near the origin position by which the Hall sensor 65 and thepair of magnets 64 are positioned close to each other. Hence, in analternative embodiment, the threshold value P0′ is set based ondetection results (of the position of the slider 57) when the slider 57is positioned 4 through 1 steps from the origin position during thebackward stroke of the reciprocating motion of the slider 57 todetermine a distance B of the slider 57 when the slider 57 moves threesteps. Accordingly, a value B/3 of the moving distance (stepwise movingdistance per one step) of the slider 57 that is multiplied by theabove-mentioned coefficient in the range of 0.3 to 0.9, preferably 0.7,can be substituted for ΔA when setting the threshold value P0′.

Furthermore, in another embodiment, the value B/3 of the moving distance(stepwise moving distance per one step) of the slider 57 is set to ΔB,and the following processes are performed.

In FIGS. 9 and 10, the detection position of the slider 57 becomes lessthan the threshold value P0′ when the stepping motor 53 is excited withthe excitation pattern (0) at the sixteenth pulse. From this state, thestepping motor 53 is held for a predetermined period of time t3 and,immediately before this holding is released, the position of the slider57 (see P3 shown in FIG. 10) is detected and stored in memory.Subsequently, the position of the slider 57 (see P4 shown in FIG. 10) isagain detected and stored in memory upon a lapse of a predeterminedperiod of time t4 from the moment at which the holding of the steppingmotor 53 is released. The difference between the positions P3 and P4 ofthe slider 57 is greater than a half of the value B/3 of the movingdistance (stepwise moving distance per one step) of the slider 57 andless than B/3 multiplied by 1.5 (B/3×1.5); and accordingly, theexcitation pattern subsequent to the excitation pattern at the time thedetection position of the slider 57 becomes less than the thresholdvalue P0′ is determined to be the initial excitation pattern (NO.).Namely, in this particular case the initial excitation pattern is theexcitation pattern (3) that follows the excitation pattern (0) of thefree state.

Thereafter, when a photographing operation is performed, namely, whenthe diaphragm apparatus 113 of the interchangeable lens 100 is driven tooperate the diaphragm stop-down operation thereof, the stepping motor 53is excited (energized) starting from the initial excitation pattern (3),and thereafter switches to the excitation pattern (0), the excitationpattern (1), the excitation pattern (2), etc . Although the excitationoperation should originally start from the subsequent excitation pattern(0), the reason why the excitation operation starts from the initialexcitation pattern (3) is to return the stepping motor 53 to theposition of the excitation pattern (3) regardless of the stop positionof the stepping motor 53 because the stepping motor 53 is sometimes atrest at a position beyond the position of the initial excitation pattern(3) toward the position of the excitation pattern (0). The excitationpattern at the moment the detection position of the slider 57 becomesless than the threshold value P0′ simply becomes the initial excitationpattern in the case where the difference between the positions P3 and P4of the slider 57 is less than a half of the ΔB.

Accordingly, by stopping the stepping motor 53 upon the detectionposition of the slider 57 becoming less than the threshold value P0′ andby finding the excitation pattern at this stopped position of thestepping motor 53, the excitation pattern, of the stepping motor 53,that should be excited in the subsequent actuation of the stepping motor53 can be determined.

In this manner, according to the present embodiment, the stepping motor53 is stopped not only before the slider 57 stops by a mechanicalcollision but also at a position less than one step to the originposition. Therefore, since the slider 57 returns to a mechanicalcollision position thereof, where the slider 57 stops by a mechanicalcollision, while driving the lead screw 55, the stepping motor 53 andthe diaphragm apparatus 113 of the interchangeable lens 100 by thebiasing force of the biasing spring 67 by a distance less than one stepof the stepping motor 53, the initial excitation pattern (NO.) of thestepping motor 53 can be obtained with precision.

The origin-position initialization process will be hereinafter discussedin detail with reference further to the flow charts shown in FIGS. 11Athrough 14. The origin-position initialization process is controlled bythe CPU 45 of the camera body 10. Control enters the origin-positioninitialization process upon the power being turned ON by switching ONthe power switch 23 of the camera body 10. Upon completion of theorigin-position initialization process, control enters a normalphotography process. In the following description, it is assumed thatthe interchangeable lens 100 is already attached on the camera body 10.

Upon control entering the origin-position initialization process,various initial setting operations are performed at steps S101 and S103.At step S101, an INIT termination flag is reset (=0) and variables areinitialized; thereafter the voltage of the Hall sensor 65 which isdetected before the stepping motor 53 is excited is detected and A/Dconverted, and the digital value (A/D value) thus obtained is stored inmemory as an origin-position detection value (detection position) P0. Atstep S103, the initial excitation pattern (NO.) is set to (0) and aremaining drive step number is set to 8. The origin position value P0represents the current stop position of the slider 57 and is utilized asthe origin position of the slider 57. The remaining drive step numberrepresents the number of the remaining steps for driving the steppingmotor 53 in the diaphragm stop-down direction in the forward stroke inthe origin-position initialization process; in this embodiment thestepping motor 53 is driven eight steps. After completion of the abovedescribed initial setting operations, a forward-stroke loop process atsteps S105 through 5127 is performed.

First, it is determined whether or not the remaining drive step numberis 0 (step S105). Since the remaining drive step number is not 0 (NO atstep S105) when control first enters the operation at step S105, it isdetermined whether or not the remaining drive step number is 4 (stepS107). The remaining drive step number 4 corresponds to one of the tworeference positions at which the moving distance of the slider 57 bythree steps is detected. Since the remaining drive step number is not 4when control first enters the operation (NO at step S107), control skipsthe operation at step S109 and proceeds to step S111.

At step S111 it is determined whether or not the remaining drive stepnumber is 1. The remaining drive step number 1 corresponds to the otherof the two reference positions at which the moving distance of theslider 57 by three steps is detected. Since the remaining drive stepnumber is not 1 when control first enters the operation at step S111 (NOat step S111), control skips the operation at step S113 and proceeds tostep S115.

At step S115, a former excitation pattern (NO.) is set to the currentexcitation pattern (NO.). The former excitation pattern (NO.) is avariable for the previous excitation pattern (NO.). The currentexcitation pattern (NO.) is a variable for the excitation pattern (NO.)with which the stepping motor 53 is about to be excited or currentlyexcited. Since the current excitation pattern (NO.) is (0) when controlfirst enters the operation at step S115, the former excitation pattern(NO.) is set to (0). Subsequently, the stepping motor 53 is excited withthe current excitation pattern (NO.) (step S117). Although the steppingmotor 53 is excited with the current excitation pattern (0) for thefirst time, the stepping motor 53 does not rotate if at rest at theposition of the excitation pattern (0), the stepping motor 53 rotatesone step in the diaphragm stop-down direction if at rest at the positionof the excitation pattern (3), the stepping motor 53 attempts to (butcannot) rotate one step in the diaphragm opening direction if at rest atthe position of the excitation pattern (1), or the rotational directionof the stepping motor 53 is undefined if at rest at the position of theexcitation pattern (2). Subsequently, it is determined whether or notthe current excitation pattern is (3) (step S119). If the currentexcitation pattern is not (3) (NO at step S119), the current excitationpattern (NO.) is incremented by 1 (step S121), whereas the excitationpattern (NO.) is set to (0) (step S123) if the current excitationpattern (NO.) is (3) (if YES at step S119). Since the current excitationpattern (NO.) is a recurring number from (0) to (3), the operation atstep S123 is for resetting the excitation pattern (3) to (0) if thecurrent excitation pattern (NO.) is (3). Since the current excitationpattern (NO.) is (0) when control first enters the operation at stepS121, the current excitation pattern (NO.) is incremented by 1 to become(1).

Subsequently, the remaining drive step number is decremented by 1 (stepS125) and control waits for a fixed period of time t1 (ms) (step S127).Upon a lapse of this fixed period of time t1, control returns to stepS105. This process for waiting this fixed period of time t1 constitutesthe duration time for holding the energization (excitation) at eachexcitation pattern (NO.).

The operations at steps S105 through S127 are repeated until it isdetermined at step S105 that the remaining drive pulse number is 0. Inthe forward-stroke loop process, if it is determined at step S107 thatthe remaining drive pulse number is 4 (if YES at step S107), thedetection value of the Hall sensor 65 is A/D converted and stored inmemory as a detection value P1 (step S109). Additionally, if it isdetermined at step S111 that the remaining drive pulse number is 1 (ifYES at step S111), the detection value of the Hall sensor 65 is A/Dconverted and stored in memory as a detection value P2 (step S113).

Upon the remaining drive pulse number becoming 0 (if YES at step S105),control proceeds to step S129 (see FIG. 11B). The process from step S129onwards is a backward-stroke loop process in which the stepping motor 53is driven in the diaphragm opening direction (toward the originposition) to return the slider 57 to the origin position. The reason whythe moving distance (moving amount) of the slider 57 per one step isdetermined from the detection value P1 of the Hall sensor 65 obtained atthe time the remaining drive step number is 4 at steps S107 and S109,and the reason why the detection value P2 of the Hall sensor 65 obtainedat the time the remaining drive step number is 1 at steps S111 and S113(i.e., at the time the stepping motor 53 is driven three steps), is todetermine the moving distance of the slider 57 per one step with higherprecision by detecting the position of the slider 57 after the steppingmotor 53 is driven by one secure step by switching the excitationpattern upon the excitation pattern has been switched by full cycle(i.e., the excitation pattern has been switched (0)→(1)→(2)→(3)→(0) inthat order) from the commencement of driving of the stepping motor 53.

At step S129 control waits a predetermined period of time t2 (ms). Byholding the stepping motor 53 for a period of time t1+t2 (ms) in thismanner, vibrations, etc., of moving parts such as the stepping motor 53and the slider 57 are attenuated during this holding period.

Subsequently, the value ΔA for threshold value correction is calculated(step S131).

ΔA=(P2−P1)/3×0.7

wherein “(P2−P1)” represents the distance (A) by which the slider 57 hasmoved while the stepping motor 53 rotates three steps from the remainingdrive step number 4 to the remaining drive step number 1 during theforward stroke in the origin-position initialization process, and “0.7”is a correction factor.

Subsequently, the threshold value P0′ is calculated (step S133).

P0′=P0+ΔA

wherein “ΔA” corresponds to the distance (length) from the originposition value P0.

Thereafter, the current excitation pattern (NO.) is set to the formerexcitation pattern (NO.) and the remaining drive step number is set to16 (step S135). The former excitation pattern (NO.) is the excitationpattern (NO.) which is set immediately before control enters theoperation at step S129 from the operation at step S105 and which iscurrently excited before the current excitation pattern (NO.) isincremented by 1 following the completion of the excitation operation.In the present embodiment, the excitation pattern (NO.) which iscurrently excited is the excitation pattern (3), so that the currentexcitation pattern (NO.) is set to (3). The remaining drive step numberin the backward-stroke loop process is set to be greater than that inthe forward-stroke loop process in order to reliably return the slider57 to the origin position.

Subsequently, it is determined whether the current INIT termination flagis 1 or the remaining drive step number is 0 (step S137). The INITtermination flag is a flag for terminating the origin-positioninitialization process; the origin-position initialization process isterminated if the INIT termination flag is “1” and not terminated if theINIT termination flag is “0”. In addition, in the initialization processat step S101, the INIT termination flag is cleared (set to 0). If thecurrent INIT termination flag is not 1 or the remaining drive stepnumber is not 0 (if NO at step S137), a positional signal detected bythe Hall sensor 65 is A/D converted and stored as a detection position(AD[16−REMAINING DRIVE STEP NUMBER]) (step S139). Subsequently, it isdetermined whether or not the detection position (AD[16−REMAINING DRIVESTEP NUMBER]) is equal to or less than the threshold value P0′ (stepS141). If the A/D converted detection position (AD[16−REMAINING DRIVESTEP NUMBER]) is not equal to or less than P0′ (NO at step S141), theformer excitation pattern (NO.) is set to the current excitation pattern(NO.) (step S143) and the stepping motor 53 is excited with the currentexcitation pattern (NO.) (step S145). The detection position(AD[16-REMAINING DRIVE STEP NUMBER]) represents the number of steps thatthe stepping motor 53 has been driven in the backward-stroke loopprocess.

Subsequently, it is determined whether or not the current excitationpatter (NO.) is (0) (step S147). If the current excitation patter (NO.)is not (0) (if NO at step S147), the current excitation pattern (NO.) isdecremented by 1 (step S149). If the current excitation patter (NO.) is(0) (if YES at step S147), the current excitation pattern (NO.) is setto (3) (step S151). The reason why the current excitation pattern (NO.)is set to (3) when the current excitation pattern (NO.) is (0) is tochange the excitation pattern (NO.) back to (3) after the excitationpattern (NO.) becomes (0) since the excitation pattern (NO.) recurs inthe order of (3), (2), (1), (0). Subsequently, the remaining drive stepnumber is decremented by 1 (step S153) and control waits the fixedperiod of time t1 (ms) (step S155). Upon a lapse of this fixed period oftime t1, control returns to step S137.

By repeating the above described operations at steps S137 through S155,the CPU 45 can control the stopping motor 53 to drive the stepping motor53 stepwise in the diaphragm opening direction while detecting theposition of the slider 57 via the Hall sensor 65. In the loop process atsteps S137 through S155, control waits for the current INIT terminationflag to be set to 1 or the remaining drive step number to become 0 (YESat step S137), or waits for the A/D converted detection position(AD[16−REMAINING DRIVE STEP NUMBER]) to become equal to or less than P0′(YES at step S141). Normally, the current position (AD[16−REMAININGDRIVE STEP NUMBER]) first becomes equal to or less than P0′ (YES at stepS141). This indicates that the slider 57 has returned to the positionbetween the origin position value PO and the threshold value P0′.

If it is determined at step S141 that the A/D converted detectionposition (AD[16−REMAINING DRIVE STEP NUMBER]) is equal to or less thanP0′ (YES at step S141), the initial excitation pattern (NO.) is set tothe former excitation pattern (NO.) (step S157), the INIT terminationflag is set to 1 (step S159), and control waits a first waiting time t3(ms) that is longer than the fixed period of time t1 (step S161).Namely, upon the detection position becoming equal to or less than P0′,the excitation of the stepping motor 53 is held for the first waitingtime t3 so as to be forced to stop. This forcible stop by such anexcitation holding attenuates vibrations, etc., of eachelement/component of the diaphragm control mechanism such as thestepping motor 53 and the slider 57 of the camera body 10 and thediaphragm apparatus 113 of the interchangeable lens 100.

After the slider 57 becomes stable, an energized-stop detection value P3that is obtained by A/D converting a detected output of the Hall sensor65 is stored in memory (step S163).

Thereafter, the excitation of the stepping motor 53 is released(energization thereof is cut off) to cause the stepping motor 53 toenter a free state (step S165), and control waits a second waiting timet4 (ms) (step S167). Upon the slider 57 stably stopping upon thestepping motor 53 coming to a free state in this manner, a valueobtained by A/D converting a detected output of the Hall sensor 65 isstored in memory as a free-stop detection value P4 (step S169), andcontrol returns to step S155. Control waits a second waiting time t4(ms) at step S167 in order to detect the stop position of the slider 57when the diaphragm apparatus 113 has returned to the mechanical initialstate thereof because, if the stepping motor 53 is made to enter a freestate, it is sometimes the case that the slider 57 moves to the stopposition at which the diaphragm apparatus 113 comes into a mechanicalinitial state while rotating the stepping motor 53 by the biasing forceof the biasing spring 67. Although the first waiting time t3 and thesecond waiting time t4 are set identical to each other, each of thesewaiting times is altered as required.

Upon control returning to step S155 from step S169, control waits thefixed period of time t1 (ms)) and thereupon it is determined whether thecurrent INIT termination flag is 1 or the remaining drive step number is0 (step S137). At this time the current INIT termination flag has beenset to 1 (YES at step S137), so that control proceeds to step S171 atwhich the power (excitation) of the stepping motor 53 is turned OFF.Thereafter it is determined whether or not the remaining drive stepnumber is 0 (step S173). If the remaining drive step number is 0 (if YESat step S173), control proceeds to an abnormal termination process; thisis because it is conceivable that some type of malfunction might haveoccurred if the stepping motor 53 does not return to the origin positionby being driven at the set drive step number because the number of drivesteps for the stepping motor 53 in the backward-stroke loop process isset to be greater than that in the forward-stroke loop process. Althoughnot shown in the drawings, the abnormal termination process is such aprocess as to indicate a visual sign or indication showing an abnormalstate on the display 43.

If the remaining drive step number is not 0 (if NO at step S173), avariation (amount of variation) ΔB of the detection value per one stepis determined (step S175). The variation ΔB is determined by thefollowing equation:

ΔB=(AD[16−REMAINING DRIVE STEP NUMBER −4]−AD[16−REMAINING DRIVE STEPNUMBER−1])/3.

Subsequently, it is determined whether or not the energized-stopdetection value P3 is greater than the free-stop detection value P4(step S177). Namely, it is determined whether the slider 57 has moved inthe diaphragm opening direction (YES at step S177), or has not moved inthe diaphragm opening direction or moved in the diaphragm stop-downdirection (NO at step S177) upon the stepping motor 53 entering a freestate.

[When Moved in Diaphragm Opening Direction]

If the energized-stop detection value P3 is greater than the free-stopdetection value P4 (if YES at step S177), a deviation amount ratio Δcfrom the energized-stop detection value P3 is determined at step S179 bythe following equation:

ΔC=(P3−P4)/ΔB.

If the deviation amount ratio ΔC is 1, this means that the steppingmotor 53 has rotated one step; if the deviation amount ratio ΔC exceeds1, this means that the stepping motor 53 has rotated more than one step.In regard to the rotational step of less than one step of stepping motor53, the initial excitation pattern is corrected when ΔC is 0.5 (half ofone rotational step) or more.

Thereafter, it is determined whether or not the deviation amount ratioAC is equal to or greater than 0.5 and less than 1.5 (step S181). Atstep S185 it is determined whether or not the deviation amount ratio ΔCis equal to or greater than 1.5 and less than 2.5. At step S189 it isdetermined whether or not the deviation amount ratio AC is equal to orgreater than 2.5 and less than 3.5.

If it is determined that the deviation amount ratio ΔC is equal to orgreater than 0.5 and less than 1.5 (if YES at step S181), the initialexcitation pattern (NO.) is decremented by 1 (step S183) and controlproceeds to step S209.

If it is determined that the deviation amount ratio ΔC is equal to orgreater than 1.5 and less than 2.5 (if YES at step S185), the initialexcitation pattern (NO.) is decremented by 2 (step S187) and controlproceeds to step S209.

If it is determined that the deviation amount ratio ΔC is equal to orgreater than 2.5 and less than 3.5 (if YES at step S189), the initialexcitation pattern (NO.) is decremented by 3 (step S191) and controlproceeds to step S209.

If the deviation amount ratio ΔC does not satisfy any of the above threeconditional expressions at steps S181, S185 and S189 (if NO at each stepS181, S185 and S189), i.e., if the deviation amount ratio ΔC is lessthan 0.5, no revision is made to the initial excitation pattern (NO.)(step S193) and control ends the origin-position initialization process.

Operations at steps S209 through S219 serve as a process of returningthe initial excitation pattern (NO.) from which 1, 2 or 3 has beensubtracted at step S183, S187 or 5191 to (3), (2), or (1), respectively.

If it is determined that the initial excitation pattern (NO.) is −1 (ifYES at step S209), the initial excitation pattern (NO.) is set to (3)(step S211) and control ends the origin-position initialization process.

If it is determined that the initial excitation pattern (NO.) is −2 (ifYES at step S213), the initial excitation pattern (NO.) is set to (2)(step S215) and control ends the origin-position initialization process.

If it is determined that the initial excitation pattern (NO.) is −3 (ifYES at step S217), the initial excitation pattern (NO.) is set to (1)(step S219) and control ends the origin-position initialization process.

If it is determined that the initial excitation pattern (NO.) is not anyof −1, -2 and -3, i.e., if the initial excitation pattern (NO.) is (0),(1) or (2) (if NO at each step S209, S213 and S217), control simply endsthe origin-position initialization process.

[Diaphragm Stop-Down Direction]

If the energized-stop detection value P3 is not greater than thefree-stop detection value P4 (if NO at step S177), the slider 57 is inthe process of further moving in the diaphragm opening direction fromthe energized-stop detection value P3, and accordingly, a deviationamount ratio ΔC from the free-stop detection value P4 is determined atstep S195 by the following equation:

ΔC=(P4−P3)/ΔB.

Subsequently, it is determined whether or not the deviation amount ratioΔC is equal to or greater than 0.5 and less than 1.5 (step S197). Atstep S201 it is determined whether or not the deviation amount ratio ΔCis equal to or greater than 1.5 and less than 2.5. At step S205 it isdetermined whether or not the deviation amount ratio ΔC is equal to orgreater than 2.5 and less than 3.5.

If it is determined that the deviation amount ratio ΔC is equal to orgreater than 0.5 and less than 1.5 (if YES at step S197), the initialexcitation pattern (NO.) is incremented by 1 (step S199) and controlproceeds to step S221.

If it is determined that the deviation amount ratio ΔC is equal to orgreater than 1.5 and less than 2.5 (if YES at step S201), the initialexcitation pattern (NO.) is decremented by 2 (step S203) and controlproceeds to step S221.

If it is determined that the deviation amount ratio ΔC is equal to orgreater than 2.5 and less than 3.5 (if YES at step S205), the initialexcitation pattern (NO.) is decremented by 3 (step S207) and controlproceeds to step S221.

If the deviation amount ratio ΔC does not satisfy any of the above threeconditional expressions at steps S197, S201 and 5205 (if NO at each stepS197, 5201 and S205), i.e., if the deviation amount ratio ΔC is lessthan 0.5, no revision is made to the initial excitation pattern (NO.)(step S193) and control ends the origin-position initialization process.In this manner, in the case where the absolute value of the deviationamount ratio ΔC is less than 0.5 (1/2), no revision is made to theinitial excitation pattern (NO.).

Operations at steps S221 through S231 serve as a process of returningthe initial excitation pattern (NO.) to which 1, 2 or 3 has been addedat step S199, S203 or S207 to (0), (1), or (2).

If it is determined that the initial excitation pattern (NO.) is 4 (ifYES at step S221), the initial excitation pattern (NO.) is set to (0)(step S223) and control ends the origin-position initialization process.

If it is determined that the initial excitation pattern (NO.) is 5 (ifYES at step S225), the initial excitation pattern (NO.) is set to (1)(step S227) and control ends the origin-position initialization process.

If it is determined that the initial excitation pattern (NO.) is 6 (ifYES at step S229), the initial excitation pattern (NO.) is set to (2)(step S231) and control ends the origin-position initialization process.

If it is determined that the initial excitation pattern (NO.) is not anyof 4, 5 and 6, i.e., if the initial excitation pattern (NO.) is (1), (2)or (3) (if NO at each step S221, 5225 and S229), control simply ends theorigin-position initialization process.

According to the above described origin-position initialization process,when the stepping motor 53 is driven to return to the initial stopposition after being driven eight steps in the diaphragm stop-downdirection, the driving of the stepping motor 53 is stopped upon thestepping motor 53 returning to either the initial stop position or aposition corresponding to a moving distance of the slider 57 which isless than a distance corresponding to one step. Therefore, no mechanicalcollision occurs in the diaphragm control mechanism 51 and the steppingmotor 53 is not forced to rotate in the diaphragm stop-down direction bybending or repulsion, etc., which makes it possible to precisely detectthe stop position of the stepping motor 53.

Moreover, even if the slider 57 is forced to move by a resilient biasersuch as the biasing spring 67 after the stepping motor 53 is stopped,the initial excitation pattern (NO.) is corrected based on thedifference between the distance between the position at which thestepping motor 53 is forced to stop and the position at which thestepping motor 53 naturally stops, and the determined moving distanceper one step, so that the initial excitation pattern (NO.) of thestepping motor 53 can be properly set with precision.

Although it is possible that the variation ΔB of the aforementioneddetection value per one step be substituted for the aforementioned valueΔA to simplify the origin-position initialization process, the variationΔB is not substituted by the value ΔA in this embodiment, and thevariation ΔB is calculated based on the detection value detected underthe condition that the output characteristic of the Hall sensor 65becomes linear with an optimum detection accuracy at the position wherethe remaining drive step number is 4, i.e., in the vicinity of theorigin position. Accordingly, the variation ΔB can be calculated withprecision and the excitation pattern can be grasped with precision. Inaddition, the number of steps for determining the moving distance can betwo, four or more than four.

The initial excitation pattern (0) of the stepping motor that is set bythe above described origin-position initialization process is stored inan internal memory (e.g., EEPROM) and used at a time of exposure. Inaddition, when the subsequent origin-position initialization process isperformed, it is desirable that the initial excitation pattern (0) thusstored in the internal memory be read out upon the power being turned ONor OFF to be used as the initial excitation pattern (NO.) in theorigin-position initialization process.

It is possible that the moving distance per one step be a predeterminedvalue which is stored in memory beforehand and read out and used whenthe origin-position initialization process is performed.

In addition, although the stepping motor 53 is driven a preset number ofsteps in the forward-stroke loop process in the present embodiment ofthe origin-position initialization process, it is possible that such astep number be not set in advance; for instance, it is possible todetect the position of the slider 57 while driving the stepping motor 53with predetermined excitation patterns and to terminate theforward-stroke loop process to proceed to the backward-stroke loopprocess upon the moving distance per one unit becoming equal to apredetermined distance a plurality of times in a row.

Although the position of the diaphragm control rod 19 (the slider 57) inthe sliding direction thereof is detected by the pair of magnets 64 (64a and 64 b) and the Hall sensor 65 in the above illustrated embodiment,the position of the diaphragm control rod 19 (the slider 57) can bedetected by any type of origin position detection sensor capable ofdetecting the relative or absolute position of the diaphragm control rod19 (the slider 57) within a predetermined range. In addition, it isdesirable for such a sensor to be a non-contact sensor; however, acontact type of sensor can also be used. Either type of sensor needs tobe required to have a sufficient degree of resolution and accuracy todetect a moving distance shorter than the moving distance of the slider57 by one step of movement of the stepping motor 53 with precision. Thetype of stepping motor to be used as a driving source of the diaphragmcontrol mechanism is not limited to a particular type stepping motorsuch as the stepping motor 53.

Obvious changes may be made in the specific embodiment of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

1. A diaphragm control apparatus incorporated in a camera body, to whichan interchangeable lens provided with a diaphragm apparatus isdetachably attached, said diaphragm apparatus including a diaphragmoperatively-associated rod for driving an adjustable diaphragm to openand shut said adjustable diaphragm, and said diaphragm control apparatusincluding a slider that is driven to move said diaphragmoperatively-associated rod, said diaphragm control apparatus comprising:a diaphragm control mechanism including a stepping motor and a leadscrew which is driven to rotate by said stepping motor, wherein saidslider is moved via rotation of said lead screw; a position detector,which detects a position of said slider; and a controller, whichcontrols an excitation pattern of said stepping motor, wherein saidslider is biased to move toward an initial position by a resilientbiaser, wherein, when said stepping motor is in a free state with saidinterchangeable lens attached to said camera body, said slider allowssaid diaphragm operatively-associated rod to move to said initialposition by a biasing force of said resilient biaser that biases saidslider toward said initial position while rotating said lead screw andsaid stepping motor, wherein said controller detects a position of saidslider as an origin position thereof via said position detector whensaid stepping motor is in said free state, wherein said controllerdrives said stepping motor stepwise by a predetermined number of stepsin a direction to move said slider away from said origin positionagainst said biasing force of said resilient biaser, and thereafterdrives said stepping motor stepwise in a direction to move said slidertoward said origin position while detecting a position of said slidervia said position detector, and wherein said controller performs anorigin-position initialization process which sets an initial excitationpattern of said stepping motor upon a distance from said detectedposition of said slider to said origin position becoming less than amoving distance of said slider for one step of said stepping motor. 2.The diaphragm control apparatus according to claim 1, wherein saidcontroller causes said stepping motor to enter a free state upon saiddetected position of said slider, which is detected via said positiondetector, becoming less than said moving distance, wherein saidcontroller thereafter detects a position of said slider to set saidinitial excitation pattern of said stepping motor from a differencebetween a position of said slider which is detected in an energizedstate and a position of said slider which is detected in said free stateof said stepping motor, and also from a moving distance of said sliderwhen stepping motor is driven by one step.
 3. The diaphragm controlapparatus according to claim 1, wherein said stepping motor is of a typewhich moves said slider stepwise one of toward and away from said originposition by being repeatedly energized with a plurality of excitationpatterns in one of predetermined forward and reverse orders, and whereinsaid controller commences a stepwise driving of said stepping motor withsaid slider being positioned at said origin position from said initialexcitation pattern in a forward stroke of a reciprocating motion of saidslider, and returns said slider to said origin position by repeatedlyenergizing said stepping motor with said plurality of excitationpatterns firstly a predetermined number of times in a predeterminedorder and subsequently in a reverse order in a backward stroke of saidreciprocating motion of said slider.
 4. The diaphragm control apparatusaccording to claim 3, wherein said controller detects said movingdistance by which said slider moves from said origin position by onestep of said stepping motor during said forward-stroke of saidreciprocating motion of said slider, in which said controller drivessaid stepping motor stepwise in said direction to move said slider awayfrom said origin position, to set a threshold value that is less thansaid moving distance by which said slider moves from said originposition by one step of said stepping motor, wherein, thereafter, saidcontroller detects a position of said slider each time said steppingmotor is driven by one step in said backward stroke of saidreciprocating motion of said slider, in which said controller drivessaid stepping motor stepwise in said direction to move said slidertoward said origin position, and wherein, upon said position of saidslider detected by said controller reaching a position in between saidthreshold value and said origin position, said controller detects aposition of said slider while holding energization of said steppingmotor, and thereafter cuts of f said energization of said stepping motorto cause said stepping motor to enter a free state.
 5. The diaphragmcontrol apparatus according to claim 4, wherein said position detectorcomprises at least one magnet and a Hall sensor.
 6. The diaphragmcontrol apparatus according to claim 5, wherein said slider is supportedby a slide shaft that extends parallel to said lead screw so that saidslider is freely slidable thereon, and wherein said magnet is installedonto said slider at a position between said lead screw and said slideshaft.
 7. The diaphragm control apparatus according to claim 1, whereinsaid diaphragm apparatus of said interchangeable lens comprises adiaphragm ring, positioned coaxially with an optical axis of saidinterchangeable lens, to be rotatable about said optical axis, saiddiaphragm operatively-associated rod being integrally formed with saiddiaphragm ring to project rearward from a rear end of saidinterchangeable lens, and wherein said diaphragm ring is continuouslybiased by a biaser in a direction to stop down an aperture formed bydiaphragm blades of said diaphragm apparatus.